The long-term objective of this proposal is to determine the relationship between the three-dimensional structures and the functions of the transcription factors Fos, Jun, and Fral (a Fos-related antigen). These proteins, which are components of the AP-1 transcription factor, are probably involved in the regulation of HIV latency. The specific aims are: 1) to express the intact proteins and their constituent domains in E. coli using the T7 RNA polymerase expression system, and to purify them to homogeneity; 2) to physically and functionally characterize the proteins; 3) to crystallize them; and 4) to determine their three-dimensional structures. Expression in E. coli will provide large amounts of unmodified protein, which is a requirement for crystallization. The proteins will be crystallized in specific complexes with DNA and in the absence of DNA. Then, the powerful combination of X-ray crystallography and molecular biology will be focused on these important eukaryotic transcription factors, which may play a fundamental role in the pathogenesis of AIDS.